In certain operations the product is in solution and an unwanted solid is dispersed in that solution. The unwanted material can be removed by filtration. This often result in a deep bed of solids. In most cases the solid is mechanically removed and the filter washed and cleaned. Mechanical removal is a problem because it requires manual shoveling of the material and the need to dispose of solid waste. This problem can be solved by using a solvent for the solid and dissolving it away. During the dissolution process the deep bed of solids has a tendency to collapse as it dissolves plugging the pores in the bed and impeding the dissolution time.
U.S. Pat. No. 1,101,639 teaches that a filter with the bulk of the solids removed can be cleaned by a liquid solvent for the material left caked on the filter.
Several patents (U.S. Pat. No. 4,786,418; U.S. Pat, No. 4,894,167; U.S. Pat, No. 4,172,185; and U.S. Pat, No. 4,448,693 describe using a gas mixed with a liquid to form a weak acid for regenerating ion exchange beds. In this case the bed is not dissolved but the ionic species are renewed.
U.S. Pat. No. 4,065,388 uses air pressure from externally introduced air to force water through the pores of an ion exchange bed to clean it out. The bed remains intact throughout the process and dissolution does not occur.
U.S. Pat. Nos. 4,857,211 and 2,937,069 describe the cleaning of the surface of a filter by dissolving the deposits thereon with a solvent formed from a gaseous reaction external to the bed. The majority of the material in the bed is removed by mechanical means before the treatment begins.
U.S. Pat. No. 5,217,629 involves a filter that has the bulk solids removed from catalyst particles. The insoluble catalyst particles remaining in the filter react with hydrogen peroxide to liberate oxygen bubbles that blow the filter pores clean of insoluble catalyst. The patent does not mention a deep bed of particles nor the internal opening of pores to solvent action to dissolve the deep bed efficiently.
A problem in the art is to increase the dissolution rate of a packed bed in such a way as to decrease the time required for dissolution.